A hydraulic excavator as a representative example of a construction machine generally comprises an automotive lower traveling structure, an upper revolving structure swingably mounted on the lower traveling structure, and a working mechanism mounted liftably in a front side of the upper revolving structure, and a ground excavating operation is performed by lifting up and down the working mechanism.
The upper revolving structure is configured mainly by a revolving frame as a base, a cab defining an operation room located at a left front portion of the revolving frame, a counterweight located in a rear end portion of the revolving frame to serve as a weight balance to the working mechanism, and a housing cover located in a front side of the counterweight to accommodate onboard equipments such as an engine and a hydraulic pump.
Here, the housing cover is composed of an upper surface cover, an engine cover, a left side surface cover, and a right side surface cover, for example. Further, each of the left and right side surface covers is usually configured by an openable and closable door for carrying out an inspection work on the onboard equipments. The door constituting the housing cover is usually comprised of a door body formed by using a thin steel plate member and a reinforcing member jointed on an inner side surface of the door body to enhance strength thereof (for example, see Patent Literature 1).    Patent Literature 1: Japanese Patent Laid-Open No. 2007-170130
In recent years, a demand for outer appearance beauty (design) of the construction machine has been increasing, and in regard to the door constituting the housing cover also, a door having a three-dimensional curved surface configuration is becoming mainstream. Therefore, the door body and the reinforcing member constituting the door are respectively press-formed by a press die and thereafter, are jointed with each other by spot welding.
In a case of using the press die for forming the reinforcing member, however, use of this press die requires a huge amount of expenditures, resulting in an increase in manufacturing cost of the door. On the other hand, in the conventional art for reducing the manufacturing cost of the door, there is adopted a method in which only the door body is press-formed by using the press die and the reinforcing member is formed by a bending process without use of the press die, wherein the door body and the reinforcing member are jointed by fillet welding.